Automatic volume control



Nov. 24, 1936. D MCCAA ET AL 2,061,710

AUTOMATIC VOLUME CONTROL Filed NOV. 9, 1929 4 Sheeis-Sheet l Nov. 24,1936.

D. G. MccAA ET AL 2,061,710

AUTOMATIC VOLUME CONTROL I Filed Nov. 9, 1929 4 Sheets-Sheet 2 Nov. 24,1936.

GRH) BIAS -o- D. G. MCCAA ET AL AUTOMAT I C VOLUME CONTROL Filed NOV. 9,1929 cARmER VOLTAGE. E.

l l i l l i VOLTAGE AmPLaFxcATloN' PER STAGE NTERNM. PLATE inPEnANcEGRID BIAS 4 Sheets-Sheet 3 Nov. 24, 1936. D. G MCCAA ET AL AUTQMATICVOLUME CONTROL F'iled Nov. 9, 1929 4 Sheets-Sheet 4 L CARRIER RHPLITUDEVOLTS IBOV Patented Nov. 24, 1936 AUTOMATIC VLUME CONTROL ApplicationNovember 9, 1929, Serial No. 405,964

15 Claims.

This invention relates to radio receiving systems and has particularreference to the automatic control of volume oi the output of suchsystems. Y

One of the objects oi the invention is to limit the output volume to anypredetermined level regardless ci the amplitude of the carrier waveinput to the system.

Another object is to so control the output Volume of a radio receivingsystem that strong carrier waves are reduced to a predetermined level,while carrier waves which are weaker than that level will be totallyunaffected. In other Words, unless a carrier Wave is present and ishigher than the level setting, the radio receiving system will maintainits full normal sensitivity.

A further object of the invention is to provide `a more sensitivecontrol than has heretofore been possible with systems of the prior artand which is obtained by deriving a small differential unidirectionalvoltage corresponding to the carrier voltage, amplifying thisdiilerential voltage, and then using the amplified voltage to bias thegrid or grids of one or more tubes preceding thedetector tube oi thesystem.

A still further object of the invention is to provide a sensitivevoltage control which, when incorporated with a receiving system, willfunction without producing hovvls due to the setting up of localoscillations or the leakage of undesirable oscillations from the inputinto the direct current amplifier.

Other objects will appear hereinafter.

The differential voltage is obtained by deriving a uni-directionalvoltage from the carrier in the output of a rectifying detector andopposing said voltage by an external source of unidirectionalelectro-motive force, the differential voltage being the algebraic sumof the derived voltage and the opposing voltage. 'Ihe differentialvoltage is then impressed on the grid of a direct current amplier whereit is amplified and from the output ci this tube, it is impressed on thegrid or grids of the vacuum tubes of the receiving system preceding thedetector tube. Said grids are biased in accordance with the amplitude ofthe incoming carrier Wave, that is, if a strong carrier Wave comes infrom the antenna and passes through the system, a large change platecurrent will take place in the output circuit of the detector tube,thereby producing a large differential voltage on the input of thedirect current amplifier which, vin turn, puts a large bias on the gridsof the tubes preceding the detector, thereby considerably cutting downthe (Cl. 25d-20) amplification oi said tubes. On the other hand, if aweak carrier wave is impressed on the antenna, a small differentialvoltage is derived and a less negative bias is impressed on the grids ofthe tubes preceding the detector, thereby permitting the tubes to.amplify to a greater extent. v If the carrier wave is below the levelsetting, then there is no effect on the system and no control of volumeoccurs.

Some of the features of the volume control of the present inventionwhich distinguish it from the prior art are:

1) The provision of a special radio frequency iilter in the grid circuitof the tube or tubes which are automatically biased and other filters inthe circuit winch make for the diflerence between satisfactory operationof the system and a system which would set up undue howls caused byoscillations being generated in the system or due to the feed-backeffect of the system.

(2) The use of a high impedance primary coil L' in the output circuit ofthe automatically biased tube or tubes.

(3) The use of a potentiometer voltage to buck the voltage derived in atime circuit in the plate circuit of the detector tube.,

(4) The use of a direct current amplier to increase the effect of thedifferential voltage.

(5) The use of a potentiometer carrying direct current only, instead ofa signal voltage-divider in the iinal output circuit to effect controlof output volume level. y

(6) The provision of an automatic biasing means on the grid ci thedetector tube itself.

(7) The provision of an automatic bias on all of the tubes of the systemup to and including the detector.

A clearer understanding of. the system and operation of the system willbe had from the drawings, in which Fig. 1 is a Wiring diagram of a radioreceiving system with the mcdiiications and additional apparatusrequired to carry out our invention with the use of a grid leakdetector;

Fig. 2 shows a system similar to that of Fig. l except that in place oithe grid leak detector a biased detector is used;

Fig. 3 is a graphical diagram showing the various relations between thecarrier wave voltage and the uni-directional grid biasing voltages of fthe direct current ampliiier and the radio frequency amplifiers;

Fig. 4 is a diagram similar to Fig. 3, showing the relation between thebiased voltage as compared With the voltage amplication in thaty stage,using a standard radio frequency transformer and using a radio frequencytransformer with a high impedance primary;

Fig. 5 is a diagram explaining the relations shown in Fig. fl;

Fig. 6 shows the relation between the carrier amplitude in volts and theoutput to the speaker in volts for systems of the prior art and for thesystem of our invention at various level settings; and

Fig. '7 shows a modification in Which a low voltage filament-type tube,such as a UX 199, is used as the ampliiicaticn variationy elementcorresponding to V1 of Figs. l and 2 and using a curn rent amplifyingtube, such as the UX 245 type, corresponding to V4 of Figs. 1 and 2.

Referring to Fig. l, the vacuum tubes V1 and V2 are radio frequencyamplifiers, V3 a grid leak detector tube and V4 a uni-directionalvoltage amplifier tube of the screen grid type. The tubes are shown ofthe heater type but it is obvious that the iilament type tubes may beused Without departing from the invention. In order to preventself-oscillation in this system, which may be due to the modicationsused in this invention, it is necessary to provide the grid circuit ofeach automatically biased tube with a lter system comprising condensersC1, Cz, C3 and the radio frequency chokes RFC, as in the grid circuitof. tube V1. The primary coil in the output circuit of tube V1comprises, for example, sixty turns instead of the usual fifteen turnsprovides a high impedance in the output circuit to match the impedanceof the tube V1, as hereinafter explained. A radio frequency by-passcondenser Ci is connected in series with the primary and is connected tothe cathode return through condenser Cz and the ground. In the platecircuit of the detector tube V3 is a radio frequency choke RFC and aradio frequency by-pass condenser C3, While in series with the primaryof the audio frequency transformer, is an audio frequency bypasscondenser Cv. The direct current component of the plate current of thedetector V3 is impressed on the time circuit RC which has its positiveend connected to the slider of the potentiometer P, which, in turn isconnected across a plate supply voltage of 22 volts. The negative end ofthe time circuit is connected to the grid of the tube V4. The screengrid `of the tube V4 is connected to a potential of 67 volts. The pla ofthe tube V4 is connected through resistance R1 which may be of the orderof 200,000 ohms, to a plate supply voltage of approximately 90 volts.The end of the resistance R1 adjacent the plate of tube V4 is connectedto the grid oi tube V1 through the special filter. By reason of thepote-ntial applied to the cathode, the grid of the tube V1 is arrangedto have a negative bia-s of 3 volts with respect to the cathode when nobias is produced by the vacuum tube V4. The vacuum tub-e V2 may have theusual connections or may be so arranged as to also be biased from theoutput of the tube V4. The cathodes of all of the tubes are heated bythe filaments which are supplied with alternating current from thetransformer T. It will be noted that the cathode of the detector isconnected, as is customary, to a point which is at a potential of 6volts positive with respect to the ground. The tubes V1 and V2 areneutralized by condensers C5 to prevent selfoscillation due to theinherent capacities` of the tubes, in a well-known manner. Theadjustment of the neutralizing point of condensers C5, however, isaccomplished in a manner different from that of the prior art and is asfollows: The slider of the potentiometer P is adjusted to its maximumpositive position so that no plate current flows in the tube or tubes obe neutralized and then the adjustment of condenser C5 is made ofminimum signal. rihis action occurs because a maximum positive settingon potentiometer P gives a maximum negative bias on tube V1 and,therefore, the tube is completely blocked except for the tube capacityand no plate current can flow. It is advisable to neutralize all theauton matically biased tubes in order that the cut-ofi` may be morenearly c nipletc. The neutralizing tap of the secondary of thetransformer, which has the high impedance primary, should include asmany turns to ground as the rimary does in order to neutralize over theentire frequency range.

The operation of the system is as follows2--A signal carrier Wave ofcertain average amplitude is impressed on the antenna and is ainpliiiedby 1e tubes V1 and V2 and detected by the tube V3. It is characteristicof the grid leak type of detector that with no signal, a cert-ain directcurrent flows in the plate circuit and with signal, the current in theplate circuit is reduced, the reduction depending on the voltageamplitude of the incoming carrier. This direct current is made to owthrough the resistance R which is shunted by the capacity C andcomprises what is known a time circuit, the lower end of the resistanceR being connected to the slider of the potentiometer P. The potentialbetween the cathode lead and the negative end of the potentiometer is[i5 volts. The potential across the potentiometer resistance is 22volts. Considering that a 2 milliampere i rent is ilo-Wing in the platecircuit of the detector with no carrier present, We may assume that l1,milliamperes Will flow with the carrier unde consideration present. ifWe assume a value of 0,000 ohms for resista .ce R, it is obvious thatthe voltage drop across R will be 20 volts with no signal present and l5volts when the carrier is present. Also, the potential across R will benegative on the plate of the detector tube. Upon a study of the circuitbetween the negative end of R and the negative end of the potentiometerP, it will be seen that when no carrier is present, the voltage will be20 volts negative on the grid of tube V4 with the slider at the negativeend and 2 volts positive with the slider on the positive ond of thepotentiometer. When a signal is present to the extent above mentioned,these voltages will be modified to l5 volts negative and 'l voltspositive. respectively. The negative end of the potentiometer isconnected to the cathode of the tube V4 which, if cf the UY 224 type,has such a characteristic that no current flows in the pl circuit untilthe grid is less than 2 Volts negative with respect to the cathode whenusing the plate and screen potentials indicated. Resistance R1 isconnected so that the plate current of the tube Vi ows therethrough. Asshown in the diagram, the potential drop across R1 will be negative onthe plate but, of course, if there no current fiowing, there will he nopotential drop. Con-- sidering the diiferential voltage availablebetween the grid the cathode of the tube V4, it be seen that either withor With-out signal present, the potentiometer P may be so adjusted thatthe plate current will or Will not flovv through R1 as desired. As willbe readily seen, by proper arrangement of voltage and resistance valuesapplied to tube V4. the voltage variation across R1 will be an amplifiedreproduction of the voltage across R. Considering th-at an adjustment ismade in which current flows through R1, the potential across it will beadded to that of the source marked 3 volts, which is connected betweenthe cathode and the grid of the tube V1 with the negative potential onthe grid. As has been hereinbefore stated, an increase in the negativepotential on the grid of tube V1 will reduce the amplification in thatstage and because the amplification has been reduced, the carrier willreach the detector with a lesser amplitude than has been considered. Thecurrent through the resistance R will, therefore, be changed less than1/ milliampere from its normal iiow and the voltage across the inputterminals of the tube V4 will be more negative on the grid and thechange in grid. voltage on tube V1 will be less than it was previouslyassumed. Like all electrical systems, this system will automaticallyadjust itself to give the desired output in accordance with the levelsetting of the potentiometer P.

The system including condensers C1, C2, C3 and chokes RFC prevents radiofrequency currents from entering the Aresist-ance R1 and the platecircuit of the tube V4, while the condensers C1, Cs and C7 prevent audioo'r radio frequency currents from entering the input circuit of the tubeV4. These precautions assure that no alternating current will beamplified by the tube V4.

It is important to note that during one-half cycle of the incomingcarrier wave, the grid of tube V3 goes positive and grid rectificationcurrent iiows through the leak resistor R3. The voltage set up acrossthis resistor has both .a unidirectional and an audio component. Thelatter component is applied to the grid of tube Vs which serves toamplify it. Thus audio frequency currents representing the demodulatedsignal appear across R3 due to grid rectification and these currents areapplied to tube V3 which amplifies them. It will be apparent then that astage of the system including a single vacuum tube, namely the detectortube, is provided with means for demodulating a modulated carrier, forderiving biasing potentials, and for lamplifying the demodulated signal.

In Fig. 2 is shown a modication of Fig. 1 in which a detector of thegrid bias type is substituted for the grid leak detector. The timecircuit RC is connected in the plate cathode circuit but instead ofbeing connected between the plate and the potentiometer, as in Fig. 1,it is connected between the cathode and the potentiometer with one endof the potentiometer connected to a potential of 6 volts positive in thepower supply. Because of the direction of the flow of plate currentthrough it, the potentials across resistance R will be positive towardthe detector cathode and negative towards the potentiorneter and powersupply. The positive end of the resistance R is connected to the grid oftube V4 and the negative end is connected to the grid of the detector sothat the detector is automatically biased by the time circuit RC inaccordance with the amplitude of the carrier wave. The advantages ofautomatically biasing the Idetector are that it is prevented from beingoverloaded by being automatically biased to the best point forthecarrier amplitude. The vacuum tube V1 is arranged to be biased from theoutput tube V4 in the same manner as in Fig. 1. The vacuum tube V2 is soarranged as. to also be biased from the output of the tube V4. In thisinstance, however, the grid return of V2 is connected to an intermediatepoint on the resistance R1 so that the grid of V2 is biased to a lesserextent than the grid of tube V1. With this arrangement, matched tubesare unnecessary. It will be seen that the bias on V1 is more than thatnecessary to produce zero plate current when cut-oli in tube V2 begins.It is not advisable to bias the tube before the detector unless allother tubes are arranged to cut off on a lower amplitude signal.Otherwise, distortion will occur.

Although the plate to cathode voltage of V1 is indicated as 90 volts onthe diagram, better cut-off will be obtained with 45 volts on the plateand one volt normal grid bias instead of 3 volts.

It will be noted from the connections in this figure that the action ofthe time circuit RC is to cause the grid of tube V4 to become morepositive, or, in other words, less negative with an increase in carriervoltage, thereby causing f a greater plate current to flow throughresistance R1, the greater plate current producing a greater voltagedrop to make the bias on tube V1 more negative, thereby reducing theamplication of the tube and bringing the output of tube V3 back tonormal. In other words, the action in this ligure differs from that inFig. 1 in that an increase in the carrier produces an increase in thedirect current iiow of the detector tube, while in Fig. 1, an increasein the carrier produces a corresponding decrease in the plate current ofthe detector tube, but in each case, the increase or decrease is made toaffect the grid of tube V4 in the same manner, that is, in the firstcase, an increased carrier makes the grid more negative and in thesecond case, makes it less positive, the final result being the same.

In systems of the prior art, so little voltage is developed across theRC circuit that without amplication, almost no Volume control willoccur. However, in the special case where one audio frequency amplifieronly is used between the detector and the sound reproducer, there may besuflicient voltage available across RC to properly control the grids ofV1 and V2.

In Fig. 3 is shown graphically the relation of the grid bias voltages onthe direct current ampliier tube an-d on the radio frequency amplierplotted against the carrier amplitude.

t will be noted in this figure, in which curve a represents the bias onthe grid oi tube V4 and curve b represents the bias on tube V1 of Fig.1, that with the control of the carrier level set at a certain point,there is no biasing effect on the tube V1 until the carrier voltagereaches a certain point c and then an increase in the carrier voltageproduces a corresponding increase in the grid bias on the tube V1 untilthe blocking limit is reached.

Figs. 4 and 5 explain graphically the purpose of using a high impedanceprimary in the plate circuit of tube V1. In Fig. 4, the curve erepresents the voltage amplification per stage plotted against the gridbias of that stage when a standard transformer having a low impedanceprimary is used, while curve f represents the Voltage amplication perstage against grid bias when a special transformer having a highimpedance primary is use-d. It will be noted that a bias of 11/2 Voltsgives the maximum amplification in a standard transformer represented bythe point h and an increase in bias to 3 volts produces a decrease inamplication, as designated by point i. On the other hand, in the curvef, the amplication is lower with a bias of 11/2 volts but reaches amaximum, as indicated by point g, when the normal bias is set at 3volts. It is for this reason that a high impedance primary is used inthe plate circuit of tube V1 and the normal grid bias on the tube is setat 3 volts, co 1responding to the point y in the curve e of Fig. 5. Thiscurve shows the relation of the internal plate impedance against thegrid bias of tube V1 and shows that a higher impedance occurs when ahigher negative bias is used and, therefore, it is essential to use ahigher external impedance to get maximum amplification. It is apparentthat when this type of high impedance primary is used, a lower negativevoltage is required en the grid to cut oil the signal.

In Fig. 6 are shown comparison curves for different settings of thelevel adjustment or the potentiometer P of the system of our inventionas compared to automatic volume control systems of the prior art. rihecurve A represents the output to the speaker in volts against carrieramplitude in volts when no volume control or level adjustment is used.The output lreeps on increasing with increase the carrier until theoverload point is reached, at which point, no substantial increase inoutput taires place. The curve B .shows the relation or the output tospeaker to the carrier amplitude with a level adjustment set to thelevel of the dotted curve when one tube is automatically biased inaccordance with systems of the prior art and curve C represents theoutput when two tubes are automatically biased in a simiiar manner. liothese two curves, the output continues to rise until the level F isreached, at which point, a decrease in the output is produced. With twotubes automatically biased, the curve C is produced in which a stillgreater decrease in output to the speaker is effected. In both thesecases, however, the output is not nearly as close to the limit of thelevel as when the automa ic volume control of our system is used, asrepresented by the curve D, in which only one tube is biased, the gridbias being rst amplied by the direct current ampliier before beingapplied to the tube. rihe reason that the curve D is nearer the leveladjustment than curves B and C is that the same increase in carrier asin curves E and C above the level setting would cause much more biasand, therefore, much more attenuation when an ampliiier is used, butbecause of the increased attenuation, less increase in carrier Voltagein the detector is necessary to bring the output down to the level ofthe system. The dotted curve J represents a level setting of 50% of thesetting I and curve E represents the output when reduced 50% by anoutput voltage-divider, as is generally done in systems of the priorart. The curve K represents the output when the level adjustment isdecreased 59% by means of the potentiometer P of our system. it will benoted that with a voltage-divider, peint F is brought down to the pointl-l, which shows that the output is reduced in like amount for both weakand strong carriers. ln other words, a weak Signal is cut down to thesame extent as a strong signal, whereas when a potentiometer is used,weak sig nals are unaffected, since the curve continues to rise to thepoint G without reduction in amplication and only at the pont G, whichis 50% of the previous level setting, a reduction of the volume iseffected and maintained at the level, as represented by curve l. Fromthe iigure, it will be seen that a greater advantage is obtained by ourimproved system in that a carrier which is below the level settingremains unaffected and a stronger signal is produced than with thesystems of the prior art and only carriers which are higher or strongerthan the level setting are kept at a predetermined level and are kept tothis level more closely than with other systems. Also a greater range ofcarrier amplitudes will be held constant, which is a feature ofparticular advantage in case of fading. This advantage may be readilyperceived from Fie. 6 by comparing curve OEE with curve CGK particularlyportions OH and OG, respectively. The area OGH which is cross-hatchedrepresents the advantage obtained since the system according to ourinvention represented by portion CG gives a greater output to thespeaker for the same carrier amplitudes between O--M than that obtainedby the systems of the prior art represented by the portion OH.

Fig. '7 is a modification showing a filament tube er the 'UX 199 typesubstituted for the radio frequency amplier tube V1 and a currentamplifier such as a UX 245 type, substituted for the voltage ampliiiertube Vl. In a system arranged in this manner, the reduction ofamplication is obtained by a change in current flow in the I'llament ortube V1 instead of a change in negative bias on the grid thereof. rEhefilament oi the tube is operated at rated current and the filamentcurrent is opposed by the plate current from the tube When the platecurrent from tube V4 increases, it opposes the ilament current of tubeV1 to a greater extent, reducing th-e filament temperature of the tubeand thereby reducing the amplification.

In Figs. i and 2, the resistance R1 and condenser C1 function as a timecircuit in like manner the time circuit RC, but their combined effectsare diierent, because they are isolated by the tube V4, than they wouldbe if they were directly connected in series or in parallel. Due to thearrangement of V4 with the time circuit RC in the gid circuit and thetime circuit R1, C1 in the plate circuit, a much greater time lag occursin the biasinor of tube V1 than would occur if the two time circuitswere not isolated by the tube V4. The reason for this is that R1 doesnot shunt R and that the voltage is not applied to R1, C1 until thevoltage across RC has built up to a substantial extent. r'his means thata more economical time system is produced in that the elements C and C1,R and R1 need not be large nd expensive. The limitation to the Value ofR is that if it be too large, an excessive amount of detector platevoltage is lost.

The amplified differential voltage, as derived in the above systems, maybe applied to the grid, as shown, or to the screen, the plate or thefilament of any tube preceding the detector.

While we have shown several modications of our invention for the purposeof description and illustration of its principles. of operation, it isapparent that other changes and modifications may be made thereinwithout departing from the scope of the invention. We desire, therefore,that only such limitations shall be imposed thereon as are indicated inthe appended claims.

Vile claim:

i.. In a radio receiving system comprising a plurality of vacuum tubesincluding a detector, means for automatically controlling the outputvolume of said system comprising a resistor in the plate-cathode circuitof said detector for causing a voltage drop therethrough, means foramplifying said voltage, means for causing said amplified voltage toaffect a vacuum tube preceding said detector, and a lter interposed inthe input circuit of said vacuum tube to prevent feed-back ofundesirable oscillations from the output of the detector.

2. In a radio receiving system comprising a plurality of vacuum tubesincluding a detector, means for automatically controlling the outputvolume of said system comprising a resistor in the output circuit ofsaid detector for causing a Voltage drop therethrough to affect one ofsaid vacuum tubes preceding said detector, whereby the eiiiciency of thesystem is modied, a lter interposed in the grid-cathode circuit of saidvacuum tube to prevent feed-back of undesirable oscillations from theoutput of the detectors, said filter comprising a pair of condensershaving their junction point connected to ground and to the tuningcondenser in said grid-cathode circuit, la pair of choke coils, one ofsaid choke coils having one terminal connected to the o-ther terminal ofone of said condensers and to the grid return of said Vacuum tube, andthe other choke coil having one terminal connected to the other terminalof the second condenser and to the cathode of said vacuum tube, and athird condenser connected across the remaining terminals of said chokecoils.

8. In a radio receiving system comprising a plurality of vacuum tubesconnected in cascade including a detector, means for automaticallybiasing one of the tubes preceding said detector to maintain the outputof said system constant within predetermined limits, said meanscomprising a resistor for causing a potential drop therethrough toaffect the bias on said tube preceding the detector, means formaintaining a high minimum negative bias on said tube, and a transformerassociated with the output circuit of said biased tube having a primarycoil of relatively high effective impedance to effect a quick cutoff ofsaid tube at a relatively low biasing potential.

4. In a radio receiving system comprising a plurality of vacuum tubesincluding a detector, transformers connecting said tubes in cascade,means for automatically biasing one or more of the tubes preceding saiddetector to maintain the output of said system constant withinpredetermined limits, said means comprising a resistor in the circuit ofsaid detector for causing a potential drop therethrough to aiect thebias on one or more of said tubes preceding the detector, and means formaintaining a high minimum negative bias on said tube, the transformersassociated With said biased tube or tubes having primary coils ofrelatively high effective impedance to eiiect a quick cut-ofi" on theefficiency of said tubes at relatively low biasing potentials.

5. In a carrier Wave receiving system comprising a plurality of Vacuumtubes including a signal demodulator, energized from a single source ofenergy, the method of automatically controlling the output volume ofsaid system Within predetermined limits in accordance with the amplitudeof the input carrier Wave which comprises deriving a uni-directionalvoltage from the output of the signal demodulator, applying said voltageto the grid of the signal demodulator to affect the bias thereon,simultaneously causing said voltage to affect the bias on the grid ofone of the tubes preceding the signal demodulator.

6. In a carrier Wave receiving system comprising a plurality of vacuumtubes including a detector connected in cascade, the method ofautomatically controlling the output volume of said system Withinpredetermined limits in accordance with the amplitude of the inputcarrier Wave Which comprises deriving a uni-directional voltage from thedetector tube, causing said Voltage to bias the grid of said detectortube, and simultaneously causing said voltage to affect the bias on atleast two of the vacuum tubes preceding the detector, one to a greaterextent than another, in accordance with the v-ariations of said derivedvoltage.

'7. In a carrier Wave system comprising a plurality of vacuum tubesincluding a detector, one or more of the tubes preceding the detectorbeing cf the low Voltage, low current filament type, the method ofautomatically controlling the output volume of said system Whichcomprises operating one or more of said tubes preceding said detector atthe rated value of lament current, deriving a uni-directional currentfrom the system, and causing said current to oppose to a greater orlesser extent the filament current of the tube or tubes preceding thedetector, Whereby the efliciency of said tubes is modified.

8. In a carrier Wave system comprising a plurality of vacuum tubesincluding a detector, one or more of the tubes preceding the detectorbeing of the low'voltage, low current filament type, the method ofautomatically controlling the output volume or" said system whichcomprises operating one or more of said tubes preceding the detector atthe normal rated value of filament current, deriving a uni-directionalcurrent from the plate circuit of the detector, and causing said platecurrent to affect to a greater or lesser extent the filament current ofthe tube or tubes preceding the detector, whereby the efficiency of saidtubes is modified in accordance with the amplitude of the input carrierWave.

9. In a radio receiving system comprising a plurality of vacuum tubes ofthe heater type including a detector, means for automaticallymaintaining the output volume of said system constant in spite ofvariations in the carrier Wave, comprising a time circuit connected inthe plate-cathode circuit of said detector, a voltageoperated thermionicvacuum tube having an indirectly heated cathode, a grid, a plate and ascreen electi'ode, the grid of said tube being connected to one terminalof the time circuit and the cathode connected to the other terminal ofthe time circuit thru a source of potential and a voltage-divider, theplate of said tube being connected thru a resistance to a positivesource of potential, and a connection from the junction point of theplate and resistance to the grid of one o1 the vacuum tubes precedingthe detector.

10. In a carrier Wave receiving system comprising a plurality of vacuumtubes including a detector connected in cascade, the method ofautomatically controlling the output volume of said system Withinpredetermined limits in accordance with the amplitude` of the inputcarrier wave which comprises deriving a uni-directional voltage from thedetector tube, causing Said voltage to affect the bias on one of thevacuum tubes preceding the detector to a greater extent than it does thebias on a succeeding one of said tubes preceding the detector so thatthe one tube will be blocked before the other.

l1. In a radio receiving system, means for amplifying the incomingsignals at a frequency above audibility, including a vacuum tube havinga control grid, an independent cathode, and an anode, means comprisinganother vacuum tube for deriving biasing potentials from signalsreceived by the system, means for amplifying said derived potentials,comprising a Vacuum tube having a control grid, an independent cathode,and an anode, means for supplying the amplied potentials to the controlgrid of said rst-mentioned tube to automatically control the outputlevel of the system in accordance with the received signals, and asingle source of unidirectional potential supply furnishing thenecessary normal uni-directional potentials to all of said vacuum tubes,the anode of said last-mentioned tube being energized by the samepotential as energizes the control grid of said rstmentioned tube, andthe cathode of said rstmentioned tube being energized more positivelythan the cathode of said last-mentioned tube by an amount suriioient toprovide anode energi- Zation for said last-mentioned tube.

l2. A signaling system comprising an amplifier having a cathode, anodeand control electrode, connected to a three electrode detector coupledto the output of said amplifier, which detector produces auni-directional change or" voltage dependent on the alternating signalvoltage irnpressed thereon, a volume control tube having a cathode,anode, and control electrode, a connection for coupling the said changeof voltage to the control electrode of said Volume control tube, meansfor maintaining the cathode 0f said Volurne control tube at a potentialgreatly negative relative to said amplier cathode, means for maintainingthe anode o said volume control tube at a potential normally slightlynegative relative to said amplifier cathode, a resistance in series withthe anode of said volume control tube for causing thereon acorresponding change of voltage whereby an increase in the currentsupplied to said rectier will produce an increase in the anode-cathodecurrent through said volurne control tube, and a connection from theanode of said volume control tube to the control electrode of saidamplier, whereby the amplification of said ainplier is regulatedautomatically.

13. In a signaling System, a vacuum tube ampliiier having a cathode anda control electrode, a Vacuum tube detector coupled to the output ofsaid amplier, a volume control tube coupled to the output or saiddetector, said volume control tube having a cathode and an outputelectrode, means for maintaining the cathode of said volume control tubegreatly negative relative to said amplifier cathode, means formaintaining the output electrode of said volume control tube normallyslightly negative relative to said amplier cathode, means for causingsaid output electrode to become more negative in the presence Vof anamplified signal, and a direct current connection between said outputelectrode and said control electrode, whereby the amplification of saidamplifier is regulated automatically.

14. A radio signal receiving apparatus which includes a carrier currentampliiier having a control electrode and a cathode, a detector tubehaving a grid, a cathode and an anode arranged for grid rectiiication,and connected to the output oi said amplifier, a resistor connected inthe anode circuit or said detector tube, across which is developed auni-directional rectiiied voltage which causes the voltage at said anodeto become less positive upon an increase of anode current, a volumecontrol tube having a cathode, an input and an output electrode, saidinput electrode being connected to said anode, whereby variations in thedetector anode Voltage are impressed on said input electrode, means forcausing the cathode of said volume control tube to be more positive thansaid input electrode, means for maintaining the cathode of said volumecontrol tube greatly negative relative to the cathode of said amplifier,means for maintaining said output electrode normally slightly negativerelative to the cathode of said amplier, a resistor connected betweensaid output electrode and the cathode of said volume control tube,whereby said output electrode becomes more negative when the voltage atsaid input electrode becomes more positive and a connection from saidoutput electrode to said control electrode, whereby an increase of thenegative voltage of said output electrode decreases the amplification ofsaid amplifier.

l5. A radio signal receiving apparatus which comprises a carrier currentamplifier having a cathode and a control electrode, a detector tube ofthe grid-detection type having a plate electrode, a volume control tubehaving `a cathode, an input electrode and an output electrode, aresistor connected in the plate circuit of said detector tube, aconnection from said input electrode to said plate electrode, means formaintaining the cathode of said volume control tube greatly negativerelative to said amplier cathode, means for maintaining said outputelectrode slightly negative relative to said amplifier cathode, aresistor connected between said output electrode and the cathode of saidvolume control tube, and a connection between said output electrode andsaid control electrode, Whereby an increase in the incoming signalstrength creates an increase in the negative bias on the controlelectrode of said amplifier.

DAVID G. MCCAA. REYNOLDS D. BROWN, JR.

CERTIFICATE GF CORRECTION.

Patent No. 21361571@ November 24, 1936.

'AVID Ga NCCAA, ET AL.

It is hereby Certified. that eiror appears in the printed Specificationof Jehe above numbered patent requiring oorreoion es follows: Page 5,second Column, etike ou?J lines 56 'to 68 inclusive, Comprising claimlO, and for claims now appearing *ehe patent es numbers 11, 12, 13, 14and 15 reed 10, 11; 12, 13 14- eepeetively; and that the seid. LettersPatent should 'be reed with these oozreetions therein that the Same mayconform io the reood. o Cese in the Patent Office.

SigneL and. sealed this 24th dey August, A. D. 1957.

Leslie Frazer (Seel) Acting Commissioner of Patents.

